Ether and Atoms: Hypotheses and Realities.
1. Ether:
A. Medium for light waves.
B. Maxwell’s ‘c’ assumed to be the velocity of light
with respect to the ether (and in the presence of no
other material substance).
C. Dispensed with by Einstein. Relativity accepts
light’s wave nature as a fundamental feature of the
world.
D. The contrast: Many had assumed that some
mechanical theory of the ether would underlie
Maxwell’s equations, and explain them as properties
of a family of waves that would exist in the ether, be
produced (and absorbed) by the interaction of various
forms of matter with the ether, etc.
E. Laplace: Je n’ai accune besoin de cette hypothèse.
A candidate for reality goes down in smoke.
II. Atoms.
A. Democritus: The world as made of little, indivisible
bits of matter whose shapes/properties interact to
account for the various physical goings-on. Lucretius
et al. follow along these lines.
B. Chemistry (Dalton): In the late 18th/ early 19th
centuries, Dalton proposed atomism to account for the
rule of fixed-ratios in chemistry. Chemical elements
were pure collections of a certain kind of atom, which
had a characteristic weight (feeding back into the
fixed-ratios law here).
C. Statistical Thermodynamics (Bolzmann, others): Late
19th century. Here again, the hypothesis that matter is
made up of little bits gets to do some real work.
D. Counting atoms: Here’s where the rubber met the
road in a really convincing way. We measured the
unit charge (Millikan) and compared it to the charge
on a mole of ionized gas to count the atoms in a mole.
We measured the unit mass (as determined from
Brownian motion) of a molecule and use it to count
the molecules in a mole. We soon found other
measures as well, including radioactive decay rates
and the level of radioactivity emitted by samples and
measures of the mass of alpha particles, which were
soon identified as helium nuclei. All these studies
gave us the same result (within about 1%, as of 1974)
for Avogadro’s number (the number of molecules in a
mole, or gram-molecular weight): 6.02252X1023
molecules per gram mole.
Quantum Realities:
A. The constraints (basic issues that make the
quantum world really weird):
i. The measurement problem: A measurement
result does not reflect a property that the
system has before it is measured, but instead
emerges out of an interaction between the
system and the measuring device.
ii. Non-locality: A measurement made here can
have an instantaneous effect on the state of a
particle light-years away from us.
B. The Responses: Interpretations of Quantum Theory.
1. No Deep Reality (Copenhagen 1)
There is no real quantum world ‘beneath’ the
phenomena we observe. All we have is the
apparatus of quantum theory, which allows us to
make predictions about what we will observe,
but which does not describe a reality which lies
deeper than what we observe.
2. Observer-Created Reality (Copenhagen 2)
a. The choices we make as observers (to measure
momentum rather than position, for example)
determine what properties a thing will have (and
what properties it consequently cannot have).
b. Reality as a whole is brought into being by the
act of observation.
3. Reality is undivided wholeness
Focused strongly on non-locality, this position
holds that the separations we make between
individual particles (in separate locations) are
misguided, as are the distinctions we normally
draw between observer and observed.
4. Many Worlds
Because a measurement made on a quantum
object (‘quon’) in a given state can (in general)
have a number of different outcomes, and each
of these possible outcomes has equal status from
the point of view of the theory, we must wonder
why it is that the result of a measurement is
always exactly one of these outcomes. The
many-worlds view slips past this puzzle by
proposing that every outcome occurs, but that
the world divides to make room for these
different (incompatible) results.
5. Quantum Logic
The properties of quons are connected to each
other in ways that ordinary properties are not.
We can capture the structure of these
connections in a logic different from the usual
Boolean structures of classical logic. This view
of quantum theory proposes that this is exactly
what quantum theory has to teach us: That we
have been using the wrong logic, and we have to
learn to think in terms of the new logic.
6. Neo-Realism
This view emphasizes non-locality, and as a
result is able to describe a ‘deep reality’ (as
against reality 1) in a familiar way: on this view
quons really do have position and momentum
and all the other familiar physical properties—
but these respond in complex, non-local ways to
the measurements we make, to meet the
constraints of quantum theory.
7. Consciousness-Created Reality (a narrower
version of 2)
On this view the kind of observation that’s
required is an interaction between a quon and a
conscious mind (whatever that is).
8. Heisenberg’s ‘Duplex’ world.
This last account of what quantum theory is
about distinguishes between deep reality (which
is made up of ‘semireal’ potentials) and
observed reality (in which some of these
potentials are become fully real, i.e. they are
actualized). These potentials are more real than
‘mere’ possibilities, but less real than actual
measurement results.